Very large, but rather local coot; rare except at a few lakes in the high Andes set amid barren and rocky surroundings. Often far out on deep-water lakes, where it looks rather uneventful: black overall with a pale yellowish bill. Seen up close, note the bizarre, erectile black “horn” appendage covering the bill base. Juvenile is dark sooty gray with a whitish throat. Builds remarkable nest mounds of stones topped with weeds that look like the tips of huge underwater volcanoes and take months, if not years, to complete.